1. Field of the Invention
The present invention relates generally to a direct access storage device (DASD) and more particularly to a magneto-resistive transducing head signal apparatus used in a DASD.
2. Description of the Prior Art
Various types of storage units, such as direct access storage devices (DASDs) are used to store data for known data processing systems. One often used type of DASD is a magnetic disk unit including a number of disks having surfaces with magnetic active material onto which data is written and from which data is read by magnetic read/write heads. In other types of DASDs, optical or other data storage media may be employed.
In a magnetic disk unit, the disks are formatted to define sectors and tracks upon the disk surfaces. Tracks are usually circular regions coaxial with the disk axis where data may be written, and sectors are parts of the tracks capable of storing a predetermined quantity of data written to the disk. Axially aligned tracks on the disks of a DASD are referred to as cylinders. The sectors of a DASD where blocks of data are stored have unique physical data block addresses (DBA). The disks of the DASD spin in unison around a common axis, and the transducer heads, usually one for each surface, are moved radially in unison across the disk surfaces. When data is read from or written to a physical DBA, the heads are moved into alignment with the cylinder containing the track in which the DBA is found, and the data transfer takes place as the sector or sectors of the DBA spin under the head.
Magneto-resistive (MR) transducer heads provide a significant advancement in read/write technology for DASDs. The magneto-resistive effect is a physical effect observed in certain materials, whereby electrical resistance of the material changes as it moves through a magnetic field. This effect can be used to read data recorded on the surface of a magnetic disk. The recorded data bits are in effect tiny magnets which create small magnetic fields near the disk surface. A read element comprising a magneto-resistive material flies in close proximity to the disk surface, varying the resistance of the element. Since a variable resistance can be detected with some electrical current flowing through the resistive element, the selected MR read element has a bias current flowing through the element as the head flies over disk surface. A preamplifier amplifies a change in voltage related to the change in resistance of the read element, and this is ultimately translated to data.
The chief advantage of the MR transducer head over conventional inductive head technology is that the MR read element is considerably more sensitive to small magnetic fields than an inductive element, enabling higher data recording densities. The MR transducer head includes separate read and write elements because the magneto-resistive effect cannot be used to write data on the disk surface. The write element, which is a conventional inductive element, is used for writing data.
FIG. 4 illustrates a conventional arrangement for connection of two MR transducer heads in a DASD. Each MR transducer head requires four signal wires. Two signal wires are used to carry write current to the write element and two signal wires are used to carry read current from the MR read element.
MR heads provide a very low amplitude signal. Picking up unwanted noise in the electrical signal path can cause signal degradation. A preamplifier is used early in the electrical signal path to amplify the read current and the write current. In some known DASDs, the preamplifier advantageously is positioned off the actuator at a stationary location. Keeping the preamplifier off the actuator minimizes actuator mass to speed up access time. As shown in the prior art arrangement of FIG. 4, providing a stationary preamplifier requires the flex cable to carry the MR signal lines.
Disk drive dimensions are normally limited by a form factor, an industry standard of length, width and height dimensions. As disk drive device form factors become increasingly smaller, electrical connections to the using system can utilize an increasingly greater portion of the device form factor. With some form factors, the number of signal lines required for use with MR transducer heads would exceed the allowable space for the flex cable.
A need exists to provide an improved arrangement in a DASD for providing signal connections with MR transducer heads that maintains adequate noise rejection for the read signal.